In recent years, perovskite oxide solid-solution systems based on ferroelectric Pb(Zn1/3Nb2/3)O3 (PZN), such as (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT), have attracted great attention due to their extremely large electromechanical strain and high dielectric constant. A PZN-PT single crystal exhibits high electromechanical coupling coefficients (k33>90%), and high piezoelectric coefficients (d33>2200 pC/N), properties which are significantly superior to those of the most widely used piezoelectric Pb(Zr,Ti)O3 (PZT) materials. Therefore, the success in developing perovskite PZN-PT bulk single crystal is thought as the most significant breakthrough in piezoelectric materials for the last few decades. In addition, as relaxor ferroelectrics, PZN-PT-based materials also exhibit a high dielectric constant and may have great potential for capacitor application.
Thin films of perovskite PZN-based materials, particularly having a tailored crystallographic orientation to obtain optimal performance properties, are in demand for application in microelectronics and micro electromechanical systems (MEMS). However, the preparation of useful perovskite PZN-based thin films is extremely challenging because of the poor stability of the perovskite phase relative to the pyrochlore phase for the PZN composition.
Previously, the perovskite phase has only been obtained and stabilized in PZN-based thin films by resorting to preparing a PZN-PT thin film composition with a high molar proportion of PbTiO3 (PT) (>50% in mole) and increasing the thickness of the thin film to above several micrometers. Furthermore, the perovskite crystallographic structure in the prepared films was not in a preferred orientation.
A randomly orientated PZN-PT film with a very low PZN composition does not demonstrate optimal characteristics for commercial applications for several reasons. Firstly, the best electromechanical property in bulk PZN-PT single crystal is exhibited with the composition around the so-called morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases, i.e. 0.9PZN-0.1PT. If the PT component of the composition is more than 50% (mole) the composition significantly shifts from the MPB, with observed degradation in the electrical and electromechanical properties.
Further, although superior electromechanical performance properties are observed along certain crystallographic directions in bulk PZN-PT single crystals, PZN-PT bulk ceramic materials with random crystallographic orientation do not exhibit the same excellent performance properties. Accordingly, a randomly orientated PZN-PT film may not be better than a PZT film in terms of its electromechanical properties.
Finally, while the perovskite phase may be stabilized in films having thicknesses beyond several micrometers, such films are too thick for many commercial applications.
The present invention seeks to overcome at least some of the aforementioned disadvantages.
It is to be understood that, although use and publications are referred to herein, such reference does not constitute an admission that any of these form a part of the common general knowledge in the art.